1. Field of the Invention
The present invention relates to an exchange control method for providing to subscribers new services that cannot be provided by a host exchange accommodating a remote switch unit (RSU) or by an outdated host exchange or an existing exchange accommodating general subscribers.
With advances in electronic exchange technology, the capacity of switching exchanges has been increasing. With this trend, the capacity of remote switch units (RSUs), installed in locations distant from their hosts, has also been increasing, and the larger the capacity, the greater the influence when subscribers accommodated in an RSU become unable to connect to subscribers outside the local exchange because of a failure, etc. of the host exchange to which the RSU is attached. There is thus a need to enable connections to be made to subscribers outside the local exchange even when the link to the host exchange is disconnected. Furthermore, when the host exchange has become outdated, it would be costly if all facilities were to be replaced with new exchange facilities that could provide exchange services including new services, and new solutions are thus needed to address such situations.
2. Description of the Related Art
FIG. 1 shows the system configuration of an exchange network; in the figure, RSU designates a remote switch unit which accommodates telephone terminals of a limited number of subscribers (for example, 1000 to 2000 subscribers). The remote switch unit (hereinafter called the RSU) is attached to a host exchange A (designated as HOST-A) via an intraoffice link. The host exchange A also accommodates subscriber lines of telephone terminals under its direct control. The host exchange A is connected to another host exchange B by an interoffice link (which includes signaling links and interoffice lines), and the host exchange A (hereinafter called the HOST-A) and the host exchange B (hereinafter called the HOST-B) are connected to other exchanges (not shown) by interoffice links.
In this configuration, the RSU is attached to the HOST-A via an intraoffice link. The intraoffice link connects between the HOST-A and the RSU, link by link and point to point, using one signal link set and a plurality of lines. In this case, the RSU is subservient to the HOST-A, and a call request by an RSU subscriber is always delivered to the HOST-A for call processing. Accordingly, when a subscriber accommodated in some other exchange (for example, the HOST-B) wants to communicate with an RSU subscriber served by the HOST-A, the communication must always be established through the HOST-A.
FIG. 2 shows an operational sequence for processing a call initiated by an RSU subscriber according to the prior art. The operational sequence shows the control procedures that the host exchange A (designated simply as HOST in FIG. 2) performs when a call is initiated by a subscriber in the RSU shown in FIG. 1. Interoffice protocol signaling is performed using ISUP. ISUP denotes ISDN User Part, a protocol used in an ISDN network based on Common Channel Signaling System No. 7, and is used to control call setup and release and additional services in the ISDN network by interworking with the layer 3 protocol of the D channel used to transfer control signals between the user and the network.
When the RSU subscriber goes off-hook (a in FIG. 2), the off-hook condition is detected by the RSU, and an off-hook signal carrying a subscriber terminal. identifier (TEI) is sent to the HOST (b in the figure) which, using an LCC (subscriber identification number) extracted from the subscriber terminal identifier (TEI), searches a calling subscriber information table and retrieves subscriber information which is analyzed. After analyzing the information, a destination number receive signal (Start Receive Digit) carrying a subscriber line trunk number (SLT) and calling subscriber identification number (LCC) is sent to the RSU to receive a destination number (called party number) (c in the figure). A line from the HOST to the calling subscriber terminal is thus connected, and a DT (dial tone) is sent to the calling subscriber, prompting the subscriber to enter a destination number (d in the figure). When the subscriber enters a destination number in response to the dial tone (e in the figure), the destination number is sent out on the connected line and delivered to the HOST, which then performs number translation and analysis and sends an IAM (Initial Address Message: A call setup message, an ISUP signaling message, that contains the destination address, the trunk information of the originating exchange, etc.) to the destination exchange serving the called subscriber (f in the figure). In FIG. 2, since the subscriber generates the dial number using a multifrequency signal (PB signal), the signal is translated and analyzed at the HOST but, in the case of dial pulses (DP), the RSU receives the pulse signal and translates it into the number before sending it to the HOST.
FIG. 3 shows an operational sequence after the AM is sent out in FIG. 2, until the line is disconnected. When the IAM message is sent from the HOST to the destination exchange, if the call can be connected at the destination, the destination exchange seizes the trunk of the called subscriber and sends an ACM (Address Complete Message: A ISUP message that indicates the completion of address signal reception) to the HOST (g in FIG. 3), signifying that ringing (transmission of a ringing signal) has started. In response, the HOST sends a path connection complete signal (Path Connect) to the RSU (h in the figure), signifying that a connection with the destination exchange has been completed, and transmits a ring back tone (RBT), sent from the destination exchange, to the calling subscriber (i in the figure). When the called subscriber goes off-hook, an ANC (Answer Charge) message signifying the start of call charging is delivered to the HOST (j in the figure), upon which the call charging is started at the originating HOST and the communication is thus started (k in the figure). Thereafter, when the communication ends and an on-hook signal from the subscriber is delivered to the HOST (1 in the figure), the HOST sends a REL (Release) message signifying the call release to the destination exchange (m in the figure), and releases the path to end the call charging. After that, when an RLC (Release Complete) message signifying the completion of the call release is received from the destination exchange (n in the figure), all resources are released.
Since RSU subscribers are controlled by the HOST exchange, as described above, if the intraoffice link in FIG. 2 connecting between the HOST-A and the RSU is severed for any reason (including the occurrence of a failure in the HOST-A), the RSU subscribers cannot communicate with the HOST-A, not to mention the subscribers beyond the HOST-A. In this case, however, intra-RSU communications can be made possible by designing a stand-alone capability into the RSU.
Such a link by link configuration can be tolerated for applications, such as RSUs serving a small number of subscribers, because the influence is limited, but when the number of subscribers to be served becomes large, communications via the host exchange cannot be provided by the stand-alone capability.
On the other hand, when a host exchange accommodating a large number of subscribers becomes outdated, or when it is desired to provide to subscribers new services that the existing exchange cannot provide, the situation could be addressed by accommodating all the existing subscribers in a newly installed exchange, but since hardware such as subscriber circuits, etc. in the existing exchange must be replaced with new hardware, this would require an enormous investment.
As described above, if new services are to be realized in an outdated host exchange accommodating a large number of subscribers, including intraoffice links to remote switch units (RSUs), large-scale hardware and software for realizing the new services have to be newly provided, and the costs involved are enormous.
Also, discarding the hardware of the outdated host exchange poses a problem in that resources are wasted.
It is an object of the present invention to provide an exchange control method that allows call processing control to be performed by a new host exchange, while making effective use of the resources of the old exchange including the remote switch unit.
According to the present invention:
(1) An old host exchange accommodating a remote switch unit or subscribers is adapted to be accommodated as a remote switch unit in a new host exchange,
the new host exchange and the old host exchange are connected in an interoffice configuration by a signaling link, each of the exchanges being provided with an emulation processor, and
the old host exchange and the new host exchange perform message editing and exchange between the respective emulation processors, and exchange control is performed in such a manner that when there occurs data or a request for basic control that is normally processed at the old host exchange, the data or request is transferred to the new host exchange, and the new host exchange processes the data or request and sends a notification to the old host exchange.
(2) In the configuration (1), the emulation processor in the old host exchange is provided with a table for translating subscriber identification information and subscriber line trunk information of the accommodated subscribers to and from subscriber identification information and subscriber line trunk information used to manage each of the subscribers at the
new host exchange, and the new host exchange manages each of the subscribers by using a number translated for the new host exchange from the subscriber information held in the old host exchange.
(3) In the configuration (1), the emulation processor in the old host exchange includes a signal receiving section for receiving signals from the accommodated subscribers or from subscribers accommodated in the remote switch unit attached to the old host exchange, a calling subscriber identification number translation section having a table for translating calling subscriber information between the old host exchange and the new host exchange, and a message processing section for performing transmission and reception of unique messages to and from the new host exchange, wherein
when an off-hook signal, destination number, or other information from a calling subscriber is received by the receiving section, the calling subscriber identification number translation section translates the identification number of the calling subscriber into the number managed at the new host exchange, and the message processing section, using the translated calling subscriber identification number, creates a message containing the received information and transmits the message to the new host exchange.
(4) In the configuration (3), when a message reporting called party ringing, call charging start, called party call release complete, or other status, is received from other exchange via a common channel signaling system signaling link, the emulation processor in the old host exchange creates a message containing information signifying the reported status and transmits the message to the new host exchange.
(5) In the configuration (1), the emulation processor in the new host exchange includes a signal receiving section for performing transmission and reception of emulation signals, a calling subscriber terminal information management section for managing subscriber information concerning the subscribers accommodated in the old host exchange, and an emulation call processing section for performing message processing and management of old host interoffice trunks, and
when the signal receiving section receives a destination number from the old host exchange, the emulation call processing section translates the destination number to extract destination-side information, retrieves an open trunk from the managed old host interoffice trunks, edits a call setup message containing information of the retrieved trunk, and transmits the message to the old host exchange.
(6) In the configuration (5), when the call setup message is received from the new host exchange, the emulation processor in the old host exchange transmits a call setup message to other exchange via the specified trunk and, when a notification signifying that the destination is ready to answer is received from that other exchange, then transmits a call-charging start message to the new host exchange.
(7) In the configuration (1), when a call setup message is received from another exchange, the emulation processor in the old host exchange transmits a message containing call setup information to the new host exchange, and
when the message is received, the emulation processor in the new host exchange checks called subscriber information, and transmits to the old host exchange a message containing information signifying the result of the check and ringing start and a message containing a ringing and path connection instruction.
(8). In the configuration (1), the old host exchange has a local exchange number of its own and is provided with a stand-alone capability for performing connection processing independently of the new host exchange, and
if the new host exchange accommodating the old host exchange fails, the old host exchange switches in the stand-alone capability to perform basic call processing, including processing of calls arising between the subscribers accommodated in the old host exchange and subscribers accommodated in other exchanges.